Thermal Curing: A Cornerstone of Composite Bonding and the Challenges of VOC Emissions

Thermal curing, the process of hardening adhesives and sealants using heat, is a ubiquitous technique in numerous industrial and product manufacturing processes. In recent years, the composites industry has garnered increasing attention, particularly in the automotive and aerospace sectors. This surge in popularity stems from the desire to reduce vehicle and aircraft weight, thereby minimizing fuel consumption and greenhouse gas emissions. Composite materials, employed in these industries, must possess exceptional tensile strengths and load-bearing capabilities to withstand extreme temperatures and pressures.

Three prominent composite bonding methods, each involving adhesive application – secondary bonding, co-bonding, and co-curing with the adhesive – predominantly differ in curing schedules. However, they all rely on heat-cure methods. In all cases, the adhesive composition must be meticulously designed to meet performance requirements under a wide range of conditions. This is why high-performance nanomaterials are commonly incorporated into adhesives for composite materials.

During the curing process, the phase transformation of epoxy resins, polyurethanes, phenol-formaldehyde resins, and other organic compounds leads to the release of significant amounts of toxic volatile organic compounds (VOCs). Stringent government regulations mandate the implementation of air pollution control equipment to prevent these VOCs from escaping into the atmosphere and causing detrimental environmental and human health effects. However, treating this VOC-laden flue gas poses a complex challenge. As the flue gas contains a diverse range of compounds with varying properties, complete absorption of VOCs from the flue gas is impractical and exorbitantly expensive. This is because multiple liquid absorbents would be required, and the subsequent desorption of these gases from the liquid phase would produce toxic waste.

In light of these limitations, high-temperature oxidation emerges as the most efficient method for VOC treatment. This process converts VOCs entirely into harmless water and carbon dioxide. Oxidation takes place in combustion chambers, where the temperature is carefully controlled based on the specific volatile compounds present, their concentration in the flue gas stream, and the lower explosion limit (LEL) of the flue gas. However, achieving 99%+ VOC removal through thermal treatment demands operating temperatures of up to 1,500-1,600°F. This translates into a significant rise in the plant's variable costs and a substantial increase in energy consumption.

In conclusion, thermal curing, a cornerstone of composite bonding, is essential for creating strong, lightweight, and durable materials. However, the production of adhesives and sealants inevitably generates VOC emissions, posing environmental and health concerns. While oxidation offers a highly efficient VOC treatment method, the high operating temperatures required place significant burdens on energy consumption and operational costs. Learn how Epcon's integrated systems can significantly reduce energy demands by harnessing thermal recycling at various stages of the process to address this challenge and ensure the sustainable production of composite materials.

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